Electromagnetic-sensitive recording medium



United States Patent US. Cl. 117-201 16 Claims ABSTRACT OF THE DISCLOSURE A sheetlike storage medium sensitive to electromagnetic energy comprising an electrically conductive backing coated with an imaging layer comprising a binder, which releases atomic halogen upon exposure to said energy, and at least one formic acid salt of a divalent first row transition metal ion.

This invention relates to new processes for storing and retrieving information using various forms of electromagnetic radiation, and to compositions and media useful therefor.

In one embodiment this invention is directed to a class of self-supporting sheet-like media preferably sensitive to radiation having wavelengths below about one micron and useful for storing information which contains at least one formic acid salt of at least one divalent first row transition metal ion which is dispersed in a substantially moisture vapor impermeable halogen-containing binder.

In another embodiment this invention relates to processes for storing information in media of the class indicated using a controlled beam of high electromagnetic energy such as an electron beam, a proton beam, an ion beam, an infrared beam, a laser beam, and the like.

In still another embodiment, this invention relates to processes for retrieving information from media of the class indicated using more than one form of instrumentally detectable physical property such as photon energy transmission, absorption, and/or emission, magnetic permeability, second electron emission ratio, and the like.

It has long been appreciated that the capacity to record and reproduce information in a given medium using a plurality of different portions of the electromagnetic spectrum is advantageous because of associated conveniences in storage density, monitoring, editing, registration and medium positioning, compatibility with a variety of communications or graphic systems, etc. Although the art has heretofore known how to record (store) in and to reproduce (retrieveor readout) information in, or from, a medium by a variety of different techniques, so far as is known to use such prior art processes and media have usually depended upon a single form of energy for recording, and upon the same or other form of energy for readout. For example, readout heretofore has been accomplished by the generation of a signal having a characteristic energy associated with a particular portion or bandwidth of the electromagnetic energy spectrum. By the present invention, however, there are provided media and methods whereby one can store and/ or retrieve information using not merely one, but a plurality of different forms of instrumentally detectable energy either sequentially or simultaneously.

It is accordingly an object of the present invention to provide an information storage and retrieval system capable of using sequentially or simultaneously, at least one controlled beam of high energy, e.g., a modulated electron beam for recording and readout, and capable of using more than'one form of energy for readout.

3,513,021 Patented May 19, 1970 Another object of this invention is to provide a process for storing and retrieving information using as a storage medium a sheet-like construction having uniformly incorporated therein at least one formic acid salt of at least one divalent first row transition metal ion dispersed in a halogen-containing binder, particularly preferred formic acid salt being those of Fe(Il), Co(II), Ni(II), Cu(II), and Zn(II) and a particularly preferred binder being a copolymer of vinylchloride and vinylacetate.

Another object of this invention is to provide a new sheet-like information storage medium and novel associated retrieval processes.

Another object of this invention is to provide such a storage medium in which a binder is employed which both provides halide radicals and serves to stabilize the formic acid salt against detrimental effects of atmospheric oxygen and/or moisture.

Another object of this invention is to provide a composition useful in the aforeindicated media, such composition employing a mixture of substantially moisture vapor impermeable halogen-containing binder and at least one formic acid salt of magnetic metal, particularly preferred formic acid salts being those of Fe(II), Co (II), and Ni(II).

Other and further objects of this invention will become apparent to those skilled in the art from a reading of the present specification taken together with the drawings.

In accordance with the above and other objects of the invention, there has been provided a composition containing a binder which includes halogen, and certain formic acid salts of divalent first row transition metal ions, which can be employed to prepare recording or storage media which when exposed to controlled high-energy beams form image-like areas corresponding to information to be stored and retrieved, which are capable of being readout in several ways.

These compositions and media form the basis for an information storage and retrieval system in which simultaneous and/ or sequential storage and readout can be accomplished, using the same or different energy sources for these purposes.

Recording of information is achieved by selectively creating in the medium during impingement of such a high-energy beam thereupon an image-like pattern which corresponds to the information being recorded. The pattern differs from the adjacent background area as respects its secondary electron emission ratio, magnetic suspec' tibility, electrical conductivity, optical properties, and/or, possibly, other physical properties.

In the drawings:

FIG. 1 diagrams one form of medium construction useful in practicing the processes of this invention before the same is used for storing information;

FIG. 2 is a view similar to FIG. 1 but showing one appearance of such medium construction after the same has been used for storing information;

FIG. 3 is a view similar to FIG. 2. but showing diagrammatically the appearance of such medium construction after the same has been subjected to heat intensification;

MEDIA AND METHODS FOR MAKING In general, storage media useful in the present invention are conveniently sheet-like and contain incorporated therein at least one formic acid salt of at least one divalent first row transition metal ion which is dispersed in a halogen-containing binder. By the term divalent first row transition metal ion as'used herein, reference is had to metal capable of existing in a divalent state as an ion and having an atomic number ranging from 25 to 30 inclusive. Such metallic ions are generically indicated by the symbol M(II) and include the following (chemical symbols being used for convenience): Mn(II), Fe(II),

Co(II), Ni(II), Cu(II) and/or Zn(II). These metal ions all characteristically have as their outer electronic shell the so-called 3d shell.

By the term magnetic reference is bad to both ferromagnetic properties (e.g., as those of iron) and ferrimagnetic properties (e.g., as those of certain of the ferrites).

These formic acid salts are initially characteristically lightly colored or white but, in a medium construction of this invention, experience both a color change and a change in secondary electron emission properties upon exposure to a source of diffeerntial electromagnetic radiation preferably having wavelengths below about one micron and having an associated energy sufficient to initiate conversion of the formic acid salt. In addition such formic acid salts containing Fe(II), Co(II), and Ni(II) become selectively magnetic upon such radiation.

In the practice of this invention it is necessary that a detectable (visually, instrumentally, or otherwise) change in magnetic or other property occur in the formic acid salt exposed to differential electromagnetic radiation. For example, if such a magnetic substance is created, in a given medium it may not necessarily be instrumentally detectable until after same is subjected to heating (i.e. heat development) as hereinafter detailed. Concurrently with heating, a color change in magnetic regions can usually be observed. However, after exposure to such source, but before such heat development, the places in such exposed medium construction where instrumentally detectable magnetic substance would appear upon heat development can characteristically be instrumentally detected by means of secondary electron emision ratio.

Instrumental detection means are known to the art and form no part of this invention. Such means as spectrophotometers, photomultipliers, Faraday balancers (for magnetic permeability), collector rings (for secondary electron emission) and the like can be used.

The formic acid salts of this invention can be represented by the following generic emprical formula:

wherein M(II) is at least one ion of a first row transition metal of atomic number 25 to 30, inclusive; in other words, an ion of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and/or Zn (II); and X is of any number from 0 through 4, inclusive, preferably either 0 or 2.

It will be appreciated that in Formula 1, (HCO represents the formate ion.

It will be further appreciated that Formula 1 is known to those skilled in the art as a formula weight presentation or as an empirical formula and refers to a definite array of anions, cations and water molecules and which indicates the essential stoichiometry involved in such array but does not reveal the total number of such entities in a molecule. The actual materials of Formula 1 are characteristically in the form of polycrystalline solids. Especially where X is two, an isomorphic series of salts is formed. It will be appreciated that a given polycrystalline mass corresponding to Formula 1 can contain a plurality of different first row transition metal ions as described above, such ions being randomly distributed throughout the crystalline mass at the individual cation sites.

One preferred group of materials within the scope of Formula 1 are those which can be converted to magnetic materials, such as ferrites by simple heating (e.g., heating in air above the decomposition temperatures). Typical decomposition temperatures are from about 200 to 400 C. Thus, by selecting the relative proportions of respective metal ions when making Formula 1 compounds, one can prepare an intermediate material which, upon thermal decomposition, produces a normal or inverse ferrite. Thus, one can make a plurality of different spinels. A particular advantage associated with magnetic materials so produced is their extremely fine crystal size. Thus, commonly individual crystals have maxim-um dimensions not greater is found in Example II of US. Pat. No. 2,688,032 by Kopelman and Wartel (1954).

The compounds of Formula 1 where X is 0 are made conveniently from the compounds where X is 2 either by in vacuo heating or by addition to anhydrous methanol of such dihydrate material.

For purposes of this invention the compounds of Formula 1 are mixed with halogen-containing binders when making storage media. Such binders are preferably substantially moisture vapor impermeable when the medium will be exposed to moist conditions in high humidity. The composition comprising formic acid salts and halogencontaining binder is then incorporated, as by coating or the like, into a medium construction so as either to form a discrete layer therein, or to be more or less uniformly distributed therethrough. Independently of position or exact composition, the combination of coordinate complex and halogen-containing binder in a medium construction is termed the imaging layer. All media of this invention contain such an imaging layer.

By the term halogen-containing binder reference is had to a cohesive non-fluid composition capable of having dispersed therein formic acid salts. It is believed that such binders release atomic halogen under electromagnetic radiation prefereably having wavelengths below about 1 micron (1 Such cohesive composition can itself be composed of more than one chemical entity. Thus, for example, a halogen-containing binder may contain materials to produce a composition adapted to disperse the formic acid salts and bind the composite imaging layer to a substrate or other layer. The term halogen has reference to chlorine, bromine, and iodine, and mixtures thereof, though chlorine and bromine are preferred, from about 20 to 80 weight percent of chlorine or the molar equivalent of bromine and/or iodine being used.

The halogen-containing binder should have low vola tility when a medium construction which is to be used in a vacuum environment (as for electron beam operation) is being prepared.

While any convenient substantially moisture vapor impermeable halogen-containing binder composition can be used, it is very much preferred for purposes of this invention to employ those which are highly halogenated polymers and which release atomic halogen upon exposure to electromagnetic radiation. Such polymers should be normally solid and of sufliciently high molecular weight to prevent their volatilization (i.e. above 1,000 and preferably above 10,000 in average molecular weight). Such a polymer preferably is film forming, and contains, in addition to hydrogen and carbon, from about 25 to about 73 Weight percent of chlorine, or the molar equivalent amount of bromine, or mixtures thereof.

Especially for ease of coating a substrate, such polymers desirably are soluble in conventional organic solvents, such as tetrahydrofuran, acetone, Z-butanone, chloroform, dichloromethane, toluene, etc., although other solvent systems can be used for the more difficultly soluble polymers, such as polymers and copolymers of vinylidene chloride. Vinylidene chloride copolymers with such monomers as the aliphatic acrylates (e.g., n-butyl acrylate, methyl acrylate, ethyl acrylate, hexyl acrylate, methyl methacrylate, beta-chloroethyl acrylate, etc.), acrylonitrile, vinyl chloride, vinyl acetate, vinyl butyrate, etc.,

which are conveniently available, are preferred highly halogenated polymers.

One especially preferred halogen-containing binder is a copolymer made from 87 weight percent vinyl chloride and 13 weight percent vinyl acetate and available commercially from the Bakelite Corporation under the trade designation VYHH.

Ethylenically unsaturated monomers with a high halogen content such as 1,l,3,3,3-pentach1or0propene-1, fiuorotrichloroethylene, 1,1-difiuro-2,2-dichloroethylene, trichloroethylene, etc. copolymerized with vinyl or vinylidene chloride or bromide or with the aliphatic acrylates can also be employed. Halogenated aromatic polymers tend to be considerably less preferred than the halogenated aliphatic polymers. With the preferred vinylidene chloride polymers the chlorine concentration ranges from about percent to 73 percent, preferably from about 40 to 70 percent by weight. With the vinyl chloride polymers the chlorine concentration ranges from about to 55 percent, preferably from about to about percent by weight of the polymer. Although the halogenated polymers are desirably deposited from solution as a film on a substrate, they may also be deposited from liquid dispersion as by spraying. With those polymers which tend to decompose slowly in the presence of ordinary light and atmospheric oxygen, anti-oxidants and other stabilizers may be added to improve good storage life.

Instead of using highly halogenated polymer systems as the halogen-containing binder, a combination of halogen free or low halogen content binder compositions with halogen containing compounds which release atomic halogen when exposed to electromagnetic radiation can be used. Such compounds may be represented by the generalized formula:

(2) ACX where A is a monovalent radical selected from the group consisting of hydrogen, chlorine, bromine, iodine, alkyl and aryl, each X is selected from the group consisting of chlorine, bromine and iodine, and C, as usual, designates carbon.

Carbon tetrabromide, bromoform, or chloroform and other highly halogenated lower alkanes are members of this class, as are CCl C Br C Cl C HBr and C6H5CBI3.

A halogen-containing compound of Formula 2 is conveniently used by admixing same with formic acid salts in a solution of a binder, such as nitrocellulose, and coating upon an appropriate substrate or base layer (see below.) Other suitable binder materials for use with Formula 2 compounds include such synthetic polymers as polyvinyl chloride; a polyvinyl chloride or polyacrylonitrile copolymer with polyvinylidene chloride; cellulose deriva' tives, such as ethyl cellulose, methyl cellulose; and the like. A host of other suitable binder materials will readily suggest themselves to those skilled in the art.

Especially when a relatively thin imaging layer is employed in a medium construction, it is commonly convenient to employ in such construction a backing layer of preformed or separately formed material. Such a backing layer can be organic or inorganic in chemical composition. Examples of suitable, commonly available organic backing layers include methyl cellulose, polymethyl methacrylate, polyethylene terephthalate, butadiene/styrene/ acrylonitrile terpolymers, polyvinyl chloride and copolymers thereof, cellulose, sisal, paper and the like.

Examples of suitable commonly available inorganic backing layers include'metal in, for instance, the form of foils (such as those of aluminum, copper, gold, foilpaper laminates, or the like), and ceramic materials.

In certain types of recording and retrieving operations within the scope of this invention, it is desirable to have associated with a recording medium, in addition to an imaging layer, an electrically conductive layer. Such an electrically conductive layer serves to dissipate an electrical charge buildup, such as can occur during recording or readout with an electron beam, whereby a higher fidelity recording is typically obtained. For example, suitably electrically-conductive layers can be obtained by vacuum vapor deposition of thin metal films such as aluminum or copper over a backing member or by coating a conductive particulate material (such as carbon black, metal particles, or the like in a polymeric binder) onto a backing layer.

Although it is preferred to have such a conductive layer adjacent to an imaging layer, it will be appreciated that it is convenient to have the imaging layer on one face of a backing layer and the conductive layer on the opposed face of such backing layer.

In certain types of recording medium constructions, it is sometimes desirable to include a fluorescent material or even a photoconductive material therein as in layered form particularly when fluorescent readout is contemplated.

In general, there appears to be no criticality in the arrangement of layers in a medium construction for practicing the teachings of the present invention. It will be appreciated that an electrically conductive material can be formulated with a backing material and that it is even possible to formulate homogeneous media wherein the halogen-containing binder, the coordinate complex and electrically conductive material (if one is used) are uniformly distributed throughout as a single layered homogeneous self-supporting construction. It will also be appreciated by those skilled in the art that some medium constructions are more preferred than others for reasons of processing, manufacture, ease in use, and the like.

As indicated above, media useful in practicing the pres ent invention are usually prepared in a sheet-like form as to permit ready handling, storage, etc.

In general, in practicing the present invention, it has been found to be preferable to use as recording media those wherein there is a discrete, separate imaging layer; such layer is preferably as thin as practicable, considering the particular recording and reproducing operations for which a given medium construction is to be utilized.

In imaging layers, it is generally convenient to employ a weight ratio of halogen-contaning binder to coordinate complex of from about 1:1 to 15:1. A more preferred ratio has been found to be about 10 parts binder to one part of coordinate complex, especially when one employs as the halogen-containing binder a vinyl chloride/vinyl acetate copolymer such as VYHH (above described) and coordinate complex(es) having a crystallite size range of from about 0.1 to I (In is equal to 10 cm.)

When using a backing layer, it is generally convenient to simply coat thereon the imaging layer in the form of a non-aqueous slurry (or solution) by conventional coating techniques and thereafter to dry and store for use. In general, conventional casting and coating procedures can be used to prepare medium constructions.

RECORDING (INFORMATION STORAGE) Briefly, to record information in accordance with the teachings of this invention using a medium as above described, one impinges a controlled beam of electromagnetic energy, preferably of high energy and preferably having a wavelength less than 1;, against one surface of such a medium.

Bearn(s) having wavelengths less than l,u are preferably employed in the practice of this invention because such wavelengths do not include infrared energy. Random application of heat energy to a medium construction during and before recording is preferably avoided.

It will be appreciated that in order to store information using a high energy beam, it is necessary in some manner to control (i.e. modulate and scan, etc.) the particular beam being used to record so as to have the capacity to differentially or selectively irradiate a surface of the storage medium so as to effect information recordation. Modulation of a beam with information to be stored can be effected by any conventional process whereby some characteristic of such a beam is varied in such a manner or to such a degree that the resulting variations or differences in beam energy as it strikes a medium being recorded upon produce selective image-like alterations in such medium.

For example, electron beams, proton beams, photon beams, ion beams, infrared beams, and laser beams can all be intensity modulated by means well known to those of ordinary skill in the art. Since the generation and control of beams of high energy is accomplished by apparatus and methods which do not form a part of the present invention and which are well known to those of ordinary skill in the art, no detailed explanation thereof is given herein. The particular type of high energy beam employed in any given instance depends, of course, upon the sensitivity and response associated with a given recording medium, upon the recording conditions, and upon a number of other variables.

It will be appreciated that, in some types of recording, it is necessary or desirable to position a recording medium in a special location or apparatus. For example, when one records upon a medium construction using an intensity modulated, scanning electron beam, it is usually convenient to place both electron gun and medium in a vacuum chamber wherein, typically, low pressures of the order of about to 10- mm. Hg pressure are conventionally employed, as those familiar with electron beam techniques will readily appreciate, but pressures greater or smaller than those indicated can be used. In general, the technology for producing the controlled beams of high energy is well known.

Obviously, the type of information which can be stored can vary very widely and includes, among others, video signals as well as telemetry data. In general, the processes of this invention are not limited by the nature of the information to be stored.

The expousre of a medium to variations in beam energy creates therein a generally latent image-like pattern of material whieh differs in secondary electron emission ratio from the surrounding background areas, such image-like pattern being a systematic characterization of the information to be recorded. Readout by secondary electron emission ratio generally is possible without heat development. Generally, for other types of readout, heat development is required.

-HEAT INTENSIFICATION OF BEAM GENERATED PATTERN Either concurrently with, or following, exposure of a medium to a controlled beam of intense electromagnetic energy in a recording operation, it is preferred to subject such medium to uniform heating. Such heating, for reasons not altogether clear, generally and usually results in an intensification of the generally latent imagelike pattern created by the incident controlled beam of energy.

Depending upon the nature of the medium being used, the nature of the controlled beam of energy and related factors, a generally latent image-like pattern created by a beam in a medium may or may not be substantially invisible and undetectable by such means as for example by visible light, or by magnetic susceptibility. In general, the greater the sensitivity of the medium being used (as respects its ability to respond to the particular beam of energy being employed for recording), and the greater the energy of such recording beam, the. greater the likelihood of producing directly by beam exposure an imagelike pattern which is visually detectable or by magnetic susceptibility.

If a visible or detectable, image-like pattern is directly created during recordation, then no further treatment of the medium may be necessary or desirable before a readout operation (described hereinafter) is undertaken. However, it has usually been found desirable and in some instances actually necessary in order to make an instrumentally detectable change in some physical property such as photon energy transmission, absorption and/or emission, magnetic susceptibility, or even secondary electron ratio to subject a prerecorded medium to heat intensification, as by exposure to a uniform zone of thermal energy. Such intensification as a result of heating can usually be observed by mere visual inspection using a source of polychromatic light.

The temperature and duration of heating can vary. In general, lower heating temperatures require longer heating times, and vice versa, in order to develop or intensify an image pattern. Heating temperatures and times are dependent upon the degree of image pattern intensification desired or necessary.

Because of the variables involved, it is not practicable to give a single time-temperature relationship suitable for all media and beam recording conditions. However, usually temperatures below 300 C. are employed and heating times are generally less than 4 minutes. Commonly, temperatures in the range of from about to C. for times of less than about one minute are suitable. Because there appears to generally be a high correlation between a visible color change associated with an image-like pattern, and its magnetic properties, it is a convenient rule of thumb to heat the, medium for a time sufficient to develop a visible color change image in irradiated or controlled beam-struck areas. A heat developed image is typically darker in color than background areas.

In general, it is preferred that, as respects a given medium and a given controlled beam of electromagnetic energy, the combination of recording and heat intensification (if the latter is used) be sufiicient to produce an instrumentally detectable. image-like pattern in such medium. Detectability of course, will vary depending upon such things as equipment limitations, fidelity, sensitivity, etc. In any case, a medium construction capable of exhibiting a signal to noise ratio of 5:1 or greater is preferred when reading out.

INFORMATION RETRIEVAL Briefly and generally, retrieval or readout from a beamexposed, and heat-intensified (if necessary or desirable) prerecorded medium as just described, is accomplished by exposing such a medium to at least one uniform field of electromagnetic energy and simultaneously detecting changes in such electromagnetic energy field created by such prerecorded medium. These energy changes can typically be in the form of photon energy (e.g., reflected, absorbed or emitted), magnetic susceptibility variations, differential secondary electron emission ratio changes, or some combination thereof. Such processes of readout are known and the conventional methods are employed in the system of this invention.

FIGURE DESCRIPTION Turning to the drawings, there is seen in FIG. 1 one embodiment of a medium construction of the invention. A substrate or backing layer 10 is coated on one. face thereof with a relatively thin (preferably below about 3 mils) imaging layer 11. The imaging layer 11 is composed of a continuous halogen-containing binder composition 12 having uniformly distributed therethrough a Formula 1 material 13.

In FIG. 2, the medium construction of FIG. 1 has been subjected to suflicient electromagnetic energy to form therein latent image areas 16 and 17. These areas or patterns can be considered to have been formed by two successive scans of an unmodulated electron beam traveling normally to the direction of the section shown.

In FIG. 3, the latent image shown in FIG. 2 has been subjected to uniform heating so as to intensify the latent image areas 16 and 17 of FIG. 2. The heat intensified image, herein designated by the respective numerals 20 and 2.1 are a different color to the eye than the adjacent background areas of the layer 11. This image may also be produced by direct exposure without heat development in media constructions having appropriate sensitivity. The areas and 21 also display a different coercivity and different secondary electron emission properties from the background area.

Typical values for the scanning electron beam for secondary electron emission readout range from about 1 to 12 kilovolts using within a range about 2 microarnperes beam current with a focused beam spot diameter on the target typically of about microns. Scanning times for a raster are typically those of commercial television.

The invention is further illustrated by reference to the following examples:

Example 1 In the preparation of manganese(II) formate dihydrate Mn(HCO -2H O, the following materials are used:

(1) 61.87 parts by weight of manganese carbonate (Manganese Chemicals Corp-Reagent Grade),

(2) 1000 parts by Weight of distilled water,

(3) 111 parts by weight of 88% aqueous formic acid (Merck Reagent), and (4) 200 parts by weight of 95% ethyl alcohol.

Item 1, 2 and 3 are mixed together, heated on a steam bath about 8 hours and filtered hot to remove insoluble material. A clear pink solution results which is vacuum evaporated on a rotating film evaporator until the light pink crystals of product Mn (I-ICO -2H O are justcovered with mother liquid. The slurry is filtered, washed with item 4, and air dried (at room temperature) to yield 67 parts by weight (68.5 yield) of manganese (II) formate dihydrate.

Example 2 Preparation of iron(II) formate dihydrate Fe(HCO -2H O following the teaching of Kopelman and Wartel, US. Pat. 2,688,032 (to Sylvania Electric Products, Inc.), Aug. 31, 1954. The following materials are used:

(1) 500 parts by weight sodium formate (Victor Chem.

Co. Protan),

(2) 138 parts by weight 88% aqueous formic acid (Merck Reagent),

(3) 1,862 parts by weight water,

(4) 1,000 parts by Weight FeSO -7H O,

(5) parts by weight 88% aqueous formic acid,

(6) 80 parts by weight ice, and

(7) 400 parts by weight water (distilled).

Items 1, 2 and 3 are mixed to form a solution containing 20.0 NaHCO and 4.86% HCO H. The resulting solution is heated to boiling before adding item 4 with stirring and then allowing the stirred reaction mixture to cool to room temperature. (If not heated, the reaction alternatively is stirred 0.5 to complete the reaction.) In either case the precipitate of very light green iron(II) formate dihydrate is filtered and washed with 515 parts by weight of 6% HCO H at 2 C. prepared by mixing items 5, 6 and 7. About 450 parts by weight (68.5% yield) of Fe(HCO -2H O is obtained.

If a purer product is desired, the 450 parts by weight of product alternatively can be placed in a large extraction thimble in a Soxhlet apparatus and continuously extracted with 2,010 parts by weight of 5% HCO H. About 60% is recovered by filtering and washing in the same manner as described above.

Example 3 In the preparation of cobalt(II) formate dihydrate Co(HCO -2H 0, the following materials are used: (1) 70 parts by weight of cobaltous carbonate (Baker and Adamson brandCode 1593Reagent Powder Assay 45-50% Co),

(2) 1,000 parts by weight of distilled water,

(3) 111 parts by weight of 88% aqueous formic acid (Merck Reagent),

(4) 1,225 parts by weight of alcohol, and,

(5) 200 parts by weight of 95 ethyl alcohol.

Items 1, 2 and 3 are mixed together, heated on a steam bath from 2-8 hours and filtered hot to remove insoluble material. A deep red solution results which after cooling is added to item 4 to form a clear red solution. On storage in a refrigerator for 48 hours 36.4 parts by weight (36% yield) of strawberry-pink cobalt(II) formate dihydrate crystals are recovered by filtering, washing with item 5 and drying in air.

The low yield in this example is attributed to a high proportion of insoluble cobalt oxide in the cobalt carbonate.

Example 4 In the preparation of nicke1(II) formate dihydrate Ni(HCO -2H O, the following materials are used:

(1) 64 parts by weight of nickelous carbonate (Baker Analyzed ReagentLot No. 27407Assay 45.6% Ni), (2) 1,200 parts by weight of distilled water, (3) 111 parts by weight of 88% aqueous formic acid, (4) 1,75 0 parts by weight of 95 ethyl alcohol, and (5) 200 parts by weight of 95 ethyl alcohol.

Using the procedure of Example 3, 84.7 parts by weight (92.7% yield) of green nickel(II) dihydrate crystals are recovered.

Example 5 In the preparation of copper(II) formate dihydrate Cu(HCO -2H 0, the following materials are used:

(1) 500 parts by weight of sodium formate (Victor Chemical Co.Protan),

(2) 104 parts by weight of 88% aqueous formic acid (Merck Reagent),

(3) 1,418 parts by weight of distilled water,

(4) 900 parts by weight of copper(II) sulfate pentahydrate (Mallinckrodt A.R.),

(5 205 parts by weight of 95 ethyl alcohol,

(6) 766 parts by weight of distilled water, and

(7) 400 parts by weight of acetone.

Items 1, 2, 3 and 4 are mixed to form a blue solution which is filtered to remove small amounts of any insoluble material. On standing 48 hours in a refrigerator some crystals deposit to form a crust which when broken with a glass rod causes copious precipitation of hydrates of both sodium sulfate and copper(II) formate. This mix ture is heated to 40 C. with stirring to dissolve the hydrated sodium sulfate and then is allowed to cool to room temperature with stirring over 16 hours.

Items 5 and 6 are mixed to form the first wash solution for the filtered product, light blue copper(II) formate dihydrate crystals, which are finally washed with item 7 and are air dried. The yield of Cu(HCO -2H O is 345.3 parts by weight (50.5%

Example 6 In the preparation of zinc(II) formate dihydrate the following materials are used:

(1) 44 parts by weight zinc oxide (Mallinckrodt),

(2) 1,200 parts by weight of distilled water,

(3) 111 parts by weight of 88% aqueous formic acid,

and

(4) 200 parts by weight of 95% ethyl alcohol.

Using the procedure of Example 1, 87 parts by weight (84% yield) of white zinc(II) formate dihydrate crystals are recovered.

1 1 Table I summarizes the observed properties of and gives the chemical evidence for the compounds of Examples 1-6 being compounds of Formula 1 wherein X is 2.

TABLE I.-PROPERTIES OF FORMULA 1 COMPOUNDS WHEREIN X IS 2 Analysis Calculated Found (wt. percent) (Wt. percent) Example Number M(II) b Color H M b C H M b 1 Mn Light pink 13.3 3.3 30.4 13.3 3.5 30.0 Fe Light green. 13.2 3. 3 30. 7 13. 3. 6 32. 4 Co Light pink" 13.0 3.3 31.9 12. 9 3. 8 31. 3 N1 Light green- 13.0 3. 2 31. 7 12. 7 3. 5 30. 7 Cu Light blue- 12. 7 3. 2 33. 5 13. 6 3. 7 32. 6 6 Zn White 12.5 3.1 34.1 12.8 3.4 34.0

An X-ray powder diifraction pattern is used to identify and verify the compound in question.

u indicates the metallic element in question.

Example 7 In the preparation of mixed iron(II), cobalt(II) formate dihydrate (Fe, Co) (CHO -2H O, the following materials are used:

(1) 24.9 parts by weight of iron(II) formate dihydrate (Example 2),

(2) 94.8 parts by weight of 88% aqueous formic acid .(Merck Reagent),

(3) 1.90 parts by weight of cobalt(II) chloride hexahydrate (Mallinckrodt A.R. Cryst. ACS),

(4) 1,650 parts by weight of distilled water, and

(5 13,800 parts by weight of absolute ethanol.

Items 1, 2, 3 and 4 are mixed and bubbled with N for 10 minutes to remove dissolved oxygen and to complete the solution of the salts. Item 5 in a large Pyrex glass jar is bubbled 'with N for 30 minutes to remove dissolved oxygen just before adding to it the first solution. The homogeneous solution which results, initially having an atomic ratio of Fe/Co of 17.3, is bubbled with N for 16 hours during which time a light pink crystalline precipitate forms. The precipitate is filtered, washed with absolute ethanol and air dried to yield 16.8 parts (79% yield) of (Fe Co (HCO '2H O. Analysis by X-ray powder diifraction pattern affords positive identification as (Fe C0 (HCO -2H O, and X-ray fluorescence establishes X as 0.9.

Example 8 In the preparation of mixed cobalt(II), iron(II), nickel (II) formate dihydrate (Co, Fe, Ni)

(HCO -2H O TABLE II.-EXAMPLES OF 12 Analyzed Reagent-Lot No. 27407Assay 45.6% (4) 220 parts by weight of 88% aqueous formic acid (Merck Reagent), and (5) 1,200 parts by weight of distilled water.

Items 1, 4 and 5 are mixed together and heated to refiux until the metallic iron dissolves. Items 2 and 3 are then added at a controlled rate to prevent frothing over by evolving CO and refluxing continued one hour after CO evolution appears to have ceased. The atomic ratio of CozFezNi is 6.7:5.1:1 in the reaction mixture. A crop of pink crystals forms in the hot solution during this time and these are recovered by filtration while the reaction mixture is still hot. After washing with 100' parts by weight of 5% aqueous formic acid followed by 50 parts by weight of acetone and drying in air 77 parts by weight (44% yield) of 0.54, ces 0.085) 2)z' 2 are obtained. Analysis by X-ray powder diifraction pattern affords positive identification as )(HCO -2H O the amount of Ni present not being detectable by this technique, and chemical analysis finds the atomic ratios of Co:Fe:Ni to be 6.3:4.4:l.

Example 9 The hot filtrate from Example 8 above on cooling deposits 45 parts by weight (25.7% yield) of a pink crystalline precipitate of 0.52 FGOAZ: lLOGS) (HCO2)2'2H2O It is recovered by filtration, washing and drying as in Example 8. Analysis by X-ray powder diffraction pattern aifords positive identification as the amount of Ni present not being detectable by this technique, and chemical analysis finds the atomic ratios of Co:Fe:Ni to be 8.016.521.

Examples 10-15 The preparation of anhydrous Formula 1 compounds (i.e. X is 0) by dehydration in methanol. Ten grams of each of the Formula 1 compounds wherein X is 2 of Examples 1 through 6 are each separately stirred with 500 ml. of anhydrous methanol under a nitrogen atmosphere for 16 hours at room temperature (25 C.) to dissolve the dihydrate salts and precipitate the corresponding anhydrous Formula 1 compounds (i.e. where X is 0). The results are indicated in Table II following.

FORMULA 1 COMPOUNDS WHEREIN X IS 0 PREPARED BY DEHYDRATION IN METHANOL B An X-ray powder difiraction pattern is used to identify and verify the compound in question. b M indlcates the metallic element in question.

the following materials are used:

(1) 21 parts by weight of iron metal powder (Mallinckrodt N.F. Electrolytic),

(2) 61.5 parts by weight of cobaltous carbonate (Baker and Adamson brandCode 1593Reagent Powder Assay 45, Co),

(3) 9.5 parts by weight of nickelous carbonate (Baker Examples 16-21 The preparation of anhydrous Formula 1 compounds (i.e., X is 0) by in vacuo heating. Each of the Formula 1 compounds wherein X is 2 of Examples 1 through 6 are heated to from about 40-100 C. at about 1 torr for several hours to remove the water of crystallization to form the corresponding anhydrous Formula I compounds (i.e.,

13 where X is The results are indicated in Table III following:

TABLE IIL-EXAMPLES OF FORMULA (1) COMPOUNDS WHERE X IS 0 PREPARED BY HEATING IN VACUO These products generally gave different X-ray powder diffraction patterns than those corresponding to Examples 10-15.

h M indicates the metallic element in question.

Examples 22-42 The above indicated compounds are each formulated into respective media suitable for electron beam recording in accordance with this invention by the following procedure:

A mixture is prepared having the following composition:

(1) 1 part by weight of Formula 1 compound;

(2) 5 parts by weight of binder (e.g., Bakelite brand VYHH, a copolymer 87% vinylchloride and 13% vinylacetate);

(3) 100-120 ball cones of stainless steel grinding media (e.g., ball cones available from Abbot Ball Company, Hartford, Conn.) per each part by weight of Formula 1 compound; and

(4) 25-50 parts by weight of dichloromethane binder solvent and dispersing medium.

The resulting mixture is tumbled for four hours in a glasslined container to produce a dispersion suitable for coat ing. Such dispersion is then knife-coated upon an aluminum foil paper laminate. This laminate comprises an aluminum foil about 1 mil thick bonded to a paper backing averaging two mils thick. The resulting aluminum foil paper laminate is transversely electrically resistive to the extent of about 1,000 ohms per square. The coating of such laminate wtih such dispersion is accomplished by passing the aluminum or obverse side of the paper over a knife coating apparatus insuch a manner that a coating is deposited on the aluminum side of the laminate while such laminate is in a vertical position. Immediately on coating, the aluminum coated side is moved so that such coated side is dried facing downwards. By so coating, the gravitational field tends to bring the Formula 1 coinpound near the surface of the coating, a condition which is desirable for electron beam recording owing to the relatively low penetrating power of electron beams of moderate energy. The coating thickness of the web coated dispersion is such that after drying in air the dry film thickness is about 0.1 mil. The final particle size of the Formula 1 compound in the medium is dependent on the initial Formula 1 compound particle size and on the contions of grinding.

In general, the smaller the final particle size of the Formula 1 compound in the medium the better is the quality of the image produced on EBR in such a medium, and the final particle size is preferably below In in average diameter. For example, in the following Table IV media of example numbers 20, 21 and 23 contain Formula 1 compound wherein X is 2 of the smaller particle size (i.e. smaller than about 1 1. in average particle diameter) and give better to best image quality (as the words good, better and best are defined for Table V). On the other hand, in the same Table IV media of ex- 14 ample numbers 19, 22 and 24 contain Formula 1 compound wherein X is 2 having larger particle sizes (i.e. averaging from 1-2.5 .t in diameter) and give only good to better image quality.

Table IV below provides a number key for identification of media so prepared.

TABLE IV Contain Formula 1 compound of the follow- Medium example number: ing example number Examples 43-63 Using a suitable electron beam recording (EBR) apparatus, information is recorded upon each of the media above described in the following manner:

Each medium is placed in the vacuum chamber with an electron beam generating and controlling apparatus wherein the pressure is maintained below about 10- torr. An electron beam having a circular cross-sectional diameter of about 25 microns in the target region where the medium being recorded upon is located. The beam has an accelerating potential of about 25 kilovolts and a resulting target current of about 40 microamperes. Each medium is exposed to three different recording conditions as follows:

( 1) a conventional commercial television frame (i.e., two interlaced fields, the duration of a single field generation being 0.0167 sec.)

(2) 15 TV frames (3) 30 TVframes After such exposure, each medium sample is removed from the vacuum chamber and subjected to uniform heat to about ISO-250 C. for a time sufficient to cause a visible image to develop in each exposed site. After an image is developed, further heating may destroy the image.

In each medium sample when a visible image was developed, such recordation was then subjected to the following conditions of readout, successively:

(1) visible photon emission (absorption) ratio, (2) secondary electron emission ratio, and (3) magnetic susceptibility ratio.

The results are tabulated in Table V below.

In this table, if readout is observed only after at least 30 TV frames exposure, the image quality is rated good; if readout is observed only after 15 TV frames or greater exposure, the image quality is rated better; and if readout is observed only after 1 TV frame or greater exposure, the image quality is rated best.

TABLE V Evaluation of Image Quality on EBB n Visible Photon Secondary Medium Emission Electron Magnetic of (Absorption) Emission Susceptibility Example Example Ratio Ratio io Number Number Readout Readout Readout Better a EBR indicates electron beam reeo rding. b Ablaek, direct image (i.e. no heat development required) is formed after 30 TV frames or greateer xposure.

We claim:

1. A sheet-like storage medium sensitive to electromagnetic radiation comprising a backing layer and an imaging layer laterally uniformly distributed relative to one face of said backing layer, said imaging layer comprising a coating of a substantially moisture vapor impermeable halogen-containing binder, which releases atomic halogen upon exposure to said radiation, and having dispersed therein an organic coordination complex comprising at least one formic acid salt of atleast one divalent first row transition metal ion.

2. The medium of claim 1 wherein said formic acid salt of at least one divalent first row transition metal ion is represented by M(II) (HCO -XH O wherein M(II) is at least one ion of a first row transition metal of atomic number 25 to 30, inclusive; and X is of any number from through 4, inclusive.

3. The medium of claim 1 wherein said formic acid salt is characterized by the following generic empirical formula:

M(II) (HCO -XH O wherein:

M(II) is at least two different ions of a first row transition metal of atomic number 25 to 30, inclusive, and X is of any number from 0 through 4, inclusive.

4. The medium of claim 1 wherein said imaging layer has a thickness less than about 3 mils.

5. The medium of claim 1 wherein the weight ratio of said halogen-containing binder to said organic coordination complex ranges from about 1:1 to :1.

6. The medium of claim 1 wherein said binder contains from about 25 to 73 weight percent of chlorine or the molar equivalent amount of bromine, or mixtures thereof.

7. The medium of claim 1 wherein the halogen-containing binder is a copolymer of vinyl chloride and vinyl acetate.

8. The medium of claim 1 wherein said formic acid salt is iron (III) formate dihydrate.

9. The medium of claim 1 wherein said formic acid salt is mixed iron (II), cobalt (II) formate dihydrate (FC,CO)1(HCO2)2'ZHZO.

10. The medium of claim 1 containing in addition to said backing layer and said imaging layer an electrically conductive layer.

11. The medium of claim 10 wherein said backing layer and said electrically conductive layer are combined into a single composite layer.

12. The medium of claim 10 wherein said backing layer comprises paper and said electrically conductive layer comprises aluminum.

13. A sheet-like storage medium sensitive to electron beam irradiation comprising an electrically conductive aluminum-paper laminate backing layer coated with an imaging layer comprising a substantially moisture vapor impermeable halogen-containing binder, which releases atomic halogenupon exposure to said irradiation, and dispersed therein an organic coordination complex comprising at least one formic acid salt of at least one divalent first row transition metal ion.

14. The medium of claim 13 wherein said halogencontaining binder is a normally solid, highly halogenated polymer having a molecular weight of at least about 1,000 and having at least weight percent of labile halogen selected from the group consisting of chlorine and bromine.

References Cited UNITED STATES PATENTS 2,637,657 5/1953 Ozols. 2,689,168 9/1954 Dovey et a1 117-235 X 2,999,035 9/1961 Sahler 117-368 2,978,414 4/1961 Harz et al. 252-6254 WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,513, Dated Maw 19. 1970 Inventor(s) N.P. Sweeney at 3.1

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 55 "use" should read us Column 3, line 12 "diffeerntisl" should read differential Column 4, line 7, delete "pre".

line 37, "preferesbly" should read preferably Column 7, line 39, "expousre" should read exposure line #1, "which" should read which Column 9, line 59, insert"hour" after 0.5.

Column 10, line 6, insert "ethyl" after 95%.

line 29, insert "formate" after (II) Column 11, line 9, second "b" should be superscript.

line 13, "Nr" should read Ni line 2l,"f '!QiZf8Q" should read --(HCO 'IZ.' 2 line &3 "Fe hould read Fe Column 13, line 14, "19.2" should read 19.0

Column 15, line 25, "greateer" should read greater line 25, "xposure" should read --exposure--.

Column 16, Claim 8, "iron (III)" should read iron (II) lines 63 and 6 "contions" should read conditions SIGNED MD SEALED SE P 29 1970 SEA! T. I r 4. Ann: I. m AM Comissionar of Patents EdwardMFlewhsgIi: Attesting Officer DRM 90-1050 10.69) USCOMM-DC 603764969 u s. sovnunm'r rnmnuc ornc: lnl o-Jls-"A 

